Method of and apparatus for electrolyzing liquids.



' H. H. DOW. METHOD OF AND APPARATUS FOR BLECTBOLYZING LI QUIDS.

APPLICATION FILED DEC. 30, 1912, 1,100,290.

Patented June 16, 1914.

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HERBERT H. DOW, 0F MIDLAND, MICHIGAN, ASSIGNOR TO THE DOW CHEMICAL COMPANY, OF MIDLAND, MICHIGAN, A CORPORATION OF MICHIGAN.

To all whom it may concern:

Be it known that 'I, HERBERT H. Dow, a citizen of the United States, and a resident of Midland, county of Midland, and State of Michigan, have invented a new and useful Improvement in Methods of and Apparatus for Electrolyzing Liquids, of which the following is a specification, the principle of the invention being herein explained and the best mode in which I have contemplated applying that principle, so as to distinguish it from other inventions.

The present improvements relate more especially to a method of electrically treating natural brines in the production of chlorin and alkali.

The object of the invention is the provision of an apparatus and method of procedure which will materially facilitate the electrolytic treatment of such brines, or of other electrolytes to which the process may be applicable, by maintaining the cathode in a solution free from alkaline-earth and iron chlorids, or other substances which, in the normal operation of the cell, would tend to decrease the yield of alkali or ultimately to defeat the purpose of the treatment entirely.

To the accomplishment of the foregoing and related ends, the invention, then, con-- sists of the steps and means hereinafter fully described and particularly pointed out in the claims.

The annexed drawing and the followin description set forth in detail one approved method of carrying out the invention, such disclosed mode, however, constituting but one of the various ways in which the principle of the invention may be used.

In said annexed drawing: Figure 1 is a more or less diagrammatic representation in cross-section of an electrolytic cell constructed in accordance with my present improvements, whereby it is adapted for carrying on my improved method of electrolysis; Fig. 2 is a section of such cell taken at rightangles to that of Fig. 1, as indicated by the line 2-2 on said figure; and Fig. 3 is a sec tion taken on the plane indicated by the line 33, Fig. 1.

In carrying out the present improved process or method, I preferably utilize the improved method of forming a porous d121 phragm in electrolytic cells set forth in U. S. Letters Patent No. 621,908, issued to me March 28, 1899. A different form of cell,

Specification of Letters Patent.

Application filed. December 30, 1912.

METHOD, OF AND APPARATUS FOR ELECTROLYZING LIQUIDS.

Patented June 16, 1914.

Serial No. 739,212.

however, is employed from that illustrated in the patent just named whereby a different dlsposition of the porous diaphragm in question is secured. This form of cell 1 illustrated in the figures of the drawing, while of general rectangular form in cross-section, s provided with a closure or cover 2 extendmg over approximately one-half the width of the cell and thence downwardly in the form of a partition 3 that depends some distance below the normal level of the liquor in the cell. The anode 41 which is preferably in the form of a carbon rod (or a series of rods, when the cell is of such longitudinal extent as to require the same), extends within the inclosed space bounded by the cover and depending partition, as shown, so that the gas, specifically chlorin in the case under conslderation, which is set free by the electrolytic action of the cell will be prevented from escaping by such inclosure, it being conducted through a passage 5 into a suitable recelving chamber, not shown. In the other, or open, portion of the cell will be disposed the cathode 6, which may consist of a series of rods, either of carbon or iron, or preferably as shown, said cathode consists of a wire mesh supported horizontally in the ortion of the cell in question and exten ing substantially the length and breadth of such portion at a suitable depth below the normal liquid level of the cell. With this disposition of parts, .I find that a porous diaphragm, of the character described in my afore-men-tioned patent, will be formed in a horizontal position extending beneath the cathode from the lower edge of the depending partition 3 to the adjacent cell wall, as indicated at 7 in the drawing. This diaphragm is made up of deposits of calcium, magnesium and iron hydrates, and subserves the same function as before. By means of it, however, it will be observed that the main body of the cell, consisting of the portion thereof lying below the plane of the depending partition, as well as that portion inclosed between said partition and the cover which supports it, is separated from the portion of the cell into which the cathode extends, so that liquids can pass from one such portion to another only by diffusion through said diaphragm.

In the present improved method, I utilize the foregoing by either initially supplying, or subsequently maintaining in the portion to maintain a catholyte substantially precipitate the soluble caustic alkali of the cell thus separated oil, into which extends the cathode, a solution other than the brine, which forms the body of the electrolyte being treated. This solution surrounding the cathode is preferably relatively pure sodium chlorid solution, although it may be a solution of any alkali chlorid which is subbrine being lighter will form a stratum super-natant on the heavier impure brine. If, thereupon, the current be passed through the cell, the diaphragm 7 will begin to form, and thereafter the pure brine be separated, as above described, from that containing the natural impurities. Instead of the foregoing procedure, if desired a little caustic may be added to the ure solution, whereupon a diaphragm will be formed even before electrolysis actually is begun.

When the alkalinity of the brine surrounding the cathode has reached the desired degree, it may be drawn off in whole or in part; or the desired degree of alkalinity may be maintained, and a continuous flow of alkaline efl'luent obtained by feeding a fresh pure (NaCl) brine to the cathode liquor .and permitting the portion of causticized catholyte thus displaced to flow out of the cell for use as such, or for further concentration to make commercial caustic soda or caustic potash. By proceeding in this manner I am enabled, fifrst, ree from impurities which will neutrallze or roduced by electrolysis at the cathode; and, second, to obtain an alkaline efiiuent as a valuable product of electrolysis se arate from the chlorin produced at the ano e. At the same time I amable to enjoy .the advantages incident to the use of an impure brine as anolyte and the diaphragm automatically formed by the precipitation of the insoluble hydrates of the impurities therein in such limited quantity as may be required to initially form and substantially maintain same effective. I

The inlet for the pure (NaCl) brine is shown at 8, the outlet 9 therefor being at the opposite end of the cell (see Fig. 2). An outlet 10 for discharging the spent solution is normally closed by a plug 11, which may be readily removed when it is desired to empty and clean out the cell. The impure brme being treated is supplied to the anode side of the cell, so as to maintain the level of liquid in the cell substantially constant. For this purpose a pipe 12, con nected with one end of the cell, may be utilized, as shown in Fig/ 3, such pipe being the exact counterpar of the ipe 8 on the cathode side, except that it is ormed with a trap in order to prevent the escape of the chlorin produced by the electrolysis. The diaphragm of precipitated hydroxids will, of course, slowly grow in thickness with the continued use of the cell, and when it becomes too heavy, the cell will be washed out and operation started over again, it being for use in this connection that the outlet 10 is provided.

Other modes of applying the principle of my invention may be employed instead of the one explained, change being made as regards the means and the steps herein disclosed, provided those stated by any one of the following claims or their equivalents be employed.

I therefore particularly point out and distinctly claim as my invention 1. In a method of electrolyzing, for the production of chlorin and alkali, a solution of chlorids that produce insoluble hydrates upon electrolysis, thesteps which consist in precipitating such hydrates to form a diaphragm between the anode and cathode, and then maintaining the latter in a solution substantially free from chlorids of the kind referred to.

2. In a method of electrolyzing, for the production of chlorin and alkali, a solution containing alkaline-earth and iron chlorids, the steps which consist in precipitating from such solution the hydrates of the bases to form a diaphragm between theanode and cathode, and then maintaining the latter in a solution substantially free from said alkaline-earth and iron chlorids.

3. In a method of electrolyzing a natural brine for the production of chlorin and alkali, such brine containing alkaline-earth and iron chlorids, the steps which consist in precipitating from such brine the hydrates of the bases named to form a diaphragm between the anode and the cathode, and then maintaining the latter in a solution substantially free from said alkaline-earth and iron chlorids.

4. In apparatus of the class described, the combination of a cell having a partition depending below the normal level of the solution therein, an anode and a cathode on the respective sides of such partition, a diaphragm formed of hydrates precipitated from the solution and extending beneath said cathode from such partition to the adjacent wall; and connections for supplying solutions 'to 'said cell above the level of said diaphragm.

5. In a method of electrolyzing an impure natural brine containing substances which precipitate as insoluble alkaline hydrates in presence of alkali formed by electrolysis, 4

precipitatesuch substances from the catholyte, thereby correspondingly lowering the specific gravity of the catholyte relatively to the anolyte; proceeding with the electrolysis of the solution; and simultaneously supplying to the catholyte a solution substantially free from substances which thus precipitate in the presence of a soluble alkali, whereby the relation in specific gravity established between the catholyte and anolyte is maintained.

7. The method of producing chlorin and alkali, which consists in electrolyzing a solution of chlorids containing considerable amounts of substances which precipitate in the presence of a soluble alkali, whereby such substances are in this manner removed from the solution as the electrolysis proceeds, and the specific gravity of the catholyte relatively to the anolyte correspondingly lowered; and then supplying to the catholyte a chlorid solution substantially free from substances which thus precipitate in the presence of a soluble alkali, whereby the relation in specific gravity established between the catholyte and anolyte is maintained.

8. The method of producing chlorin and alkali, which consists in electrolyzin alkali chlorid solution containing considerable amounts of chlorids of the alkaline earths which precipitate in the presence of I a soluble alkali so as to form from the alkaline earth hydrates precipitated in the neighborhood of the cathode, a diaphragm separating the underlying anolyte containing alkaline earth chlorids, from the overlying catholyte of lighter specific gravity, from which the alkaline earth hydrates have been precipitated; continuing the electrolysis to produce soluble alkali 1n the resulting catholyte, feeding to the anolyte alkali chlorid solution containing alkaline earth chlorids, and feeding to the catholyte alkali chlorid solution substantially free from alkaline earth chlorids.

Signed by me, this 26th day of December, 

